Pyrolytic decomposition of silicon-bearing gas in fluidized beds is an attractive process for producing polysilicon-coated granular material, such as polysilicon or polysilicon-coated germanium, due to excellent mass and heat transfer, increased surface for deposition, and continuous production. An issue in many fluidized bed reactors is the formation of large bubbles within the bed in the main reaction zone under certain conditions.
An unwanted effect of large bubbles, particularly in gas-solid systems, is that they can cause the bed to bounce violently up and down as they lift a significant fraction of the bed, then drop it suddenly. This pressure oscillation can interfere with proper operation of the bed by causing the gas velocity rate to vary, which may be harmful to optimum productivity. The pressure oscillation also causes mechanical stress to the reactor structure and any directly connected support equipment. Furthermore, large bubbles can cause the bed material to surge upward in the reactor in a phenomenon known as “slugging.” Slugging can cause ejection of at least a portion of the bed from the reactor or damage internal reactor components.
Slugging is a significant problem when bubbles reach a diameter close to the inner cross-sectional dimension of the reaction chamber. Varying the diameter of fluidized bed reactor's reaction chamber such that a narrower section is included in the reaction zone tends to reduce the amount of slugging in the fluidized bed. The varying inner cross-sectional dimensions affect the velocity of upward gas flow in the reaction chamber. A first velocity at the point of gas introduction produces bubbles having a first average size, while a second, different velocity higher up in the reaction chamber favors bubbles having a second average size. The inner cross-sectional dimension of the reaction chamber can be varied over its length to prevent or minimize the occurrence of bubbles having a size sufficient to disrupt fluidization, which may result in slugging that ejects at least a portion of the bed from the reactor and/or damages internal reactor components. A liner of varying inner cross-sectional dimension can be formed by joining liner segments of differing inner cross-sectional dimensions and inserted into the FBR reaction chamber to reduce slugging. However, a need exists for a component suitable for joining the liner segments to produce the liner.